Soundmagus vs1500 protected

[yoppi]

Transistors Q85, Q86 and Q87 are new

 

[Perry Babin]

Why were they replaced?

Are you sure that you used the correct replacements?

 

[yoppi]

Yes, the replacement is correct. Q85 and Q86 2X (MMTB4401) Q87 2T (MMTB4403)

 

[yoppi]

Hi

I have installed all the transistors (power supply and output), but it is protected again, even if Q85 is jumpered.
Any idea?

 

[Perry Babin]

If you lift Q87?

 

[yoppi]

Yes, I've removed q87 too, but it's still in protection.
The power supply and output transistors are correct. This amplifier it has my crazy.
Never an amplifier has given me as much war as this soundmagus.
Thank you very much for your help ....

 

[Perry Babin]

If you can't find the fault, post the DC voltage on all terminals of the 494 and U19.

 

[yoppi]

Q85 bridging (protection OFF) POWER SUPPLY VOLTAGE: 14,27 VDC

TL494:
PIN 1: 0V 9: 6,15V
2: 4,96V 10: 6,10V
3: 61mV 11: 14,2V
4: 0V 12: 14,2V
5: 1,467V 13: 4,96V
6: 3,558V 14: 4,96V
7: 0V 15: 2,038V
8: 14,2V 16: 0V

U19: U21:
PIN 1: 5,13V PIN1: 150mV
2: 4,96V 2: 13,67V
3: 8,33V 3: 2,72V
4: 0V 4: 0V
5: 2,529V 5: 2,86V
6: 2,194V 6: 0V
7: 5,14V 7: 14,06V
8: 14,2V 8: 14,2V

Q85 NOT bridging (protection ON)

TL494:
PIN 1: 0V 9: 123mV
2: 4,96V 10: 540mV
3: 4,52V 11: 14,2V
4: 0V 12: 14,2V
5: 1,467V 13: 4,96V
6: 3,558V 14: 4,96V
7: 0V 15: 2,038V
8: 14,2V 16: 3,97V

U19: U21:
PIN 1: 5,13V PIN1: 150mV
2: 4,96V 2: 13,67V
3: 8,33V 3: 2,72V
4: 0V 4: 0V
5: 2,529V 5: 2,70V
6: 2,194V 6: 12,36V
7: 5,14V 7: 148mV
8: 14,2V 8: 13,63V

 

[Perry Babin]

Does the amp function with the jumper on Q85?

 

[yoppi]

Yes, but removing all the transistors from the power supply.
the transistors of the power supply are all new.

 

[Perry Babin]

What do you mean by:
but removing all the transistors from the power supply.

 

[yoppi]

when you have all the transistors of the power supply installed, even jumpers when Q85 goes into protection (fixed red light, blinking blue).
if I remove all the transistors from the power supply, if jumper Q85 no longer enters protection (fixed blue light) and it has a pulse of 6v and 26khz again on pin 9 and 10 of tl494.

 

[Perry Babin]

This amp monitors the power supply. When the drive signal isn't as expected or there is no rail voltage, it will cause the protection circuit to engage. When you remove the power supply FETs, you're triggering that part of the protection circuit. That's why you have disable it.

Didn't you state that the amp was operating perfectly with the protection disabled?

 

[yoppi]

I managed to solve the problem. a cold solder in a resistance close to Q14